1. Field of the Invention
The present invention relates to hydraulic systems and, more particularly, to hydraulically controlling the amount of weight that a plow blade cutting edge bears on a surface to be plowed.
2. Background of the Prior Art
Road or grader plows are heavy pieces of equipment, often weighing 1500 or more pounds. A standard plow has a blade cutting edge, a second edge parallel to the blade cutting edge, and a concave and convex shaped body connecting the blade cutting edge with the second edge. The plow is generally mounted to a vehicle, such as a truck, with the blade cutting edge positioned adjacent a surface to be plowed, the concave shaped portion of the body facing away from a front side of a vehicle, and the second edge parallel to the surface to be plowed.
Generally, when a blade cutting edge of a plow is lowered onto a surface to be plowed, such as a concrete or asphalt road, the entire weight of the plow is distributed along the blade cutting edge of the plow. The weight of the plow on the blade cutting edge, combined with friction between the blade cutting edge and the surface being plowed, wears out the blade cutting edge of the plow, sometimes in as little as four hundred miles.
In an effort to increase the lives of plow blade cutting edges, which can be very expensive, balancing systems have been developed to reduce the amount of force exerted on the blade cutting edges of the plows. For example, U.S. Pat. No. 5,265,356 to Winter and Japanese Laid Open Publication No. 2-47413 generally disclose hydraulic systems that balance a front or mid-mounted plow.
One drawback of the prior art in general is powering balance circuits having a fixed volume pump that is PTO driven through the vehicle transmission. Because the fixed volume pump is keyed to the transmission, it must be disengaged during shifting. The result is uneven or disjointed load balancing as the transmission shifts gears and fluid pressure fluctuates. Heat is also a problem, due to the voluminous flow rate of hydraulic fluid through the pump at maximum system pressure and the corresponding horsepower draw from the engine.
To help solve the problems associated with the prior art, the present invention is directed toward a lifting, lowering, and balancing system for a plow generally including a balance circuit, a pump fluidly connected to the balance circuit, and a load sensing valve bank fluidly connected to the balance circuit and a pump, such a load sensing pump or other suitable device. An hydraulic cylinder positioned adjacent a plow vehicle is also fluidly connected to the balance circuit, the load sensing pump, and to the load sensing valve bank.
The balance circuit generally includes a two-position solenoid valve, a two-position three-way solenoid valve, a two-position four-way valve with detent, a counterbalance valve with reverse freeflow check, a pressure relieving valve, and a shuttle valve.
The load sensing valve bank generally includes a lift and lower valve, such as an all ports blocked load sensed proportional control valve, or a P blocked, A and B to T configuration valve. A drain line is fluidly connected to the relieving port of the pressure reducing relieving valve and a fluid reservoir or fluidly connected to the relieving port of the pressure reducing relieving valve, a fluid reservoir, and the shuttle valve. In the second instance, the drain line has a reduced internal diameter portion positioned between the relieving port of the pressure reducing relieving valve and the shuttle valve.
One method of balancing a plow, where the plow is attached to a hydraulic cylinder having a blind end and a port end, includes the step of:
a. pumping a non-compressible fluid into the blind end of the hydraulic cylinder to create a fluid force in the blind end of the hydraulic cylinder which is greater than zero pounds per square inch and less than an opposite force exerted on the non-compressible fluid in the blind end of the hydraulic cylinder by a weight of the plow. Pumping is generally accomplished using a pump, such as a load sensing pump fluidly connected to the hydraulic cylinder, to pump the non-compressible fluid into the blind end of the hydraulic cylinder.
Balancing a plow is generally accomplished by:
b. lowering the plow onto a surface; and
c. energizing the two-position valve.
Raising the plow while balancing includes the steps of:
d. engaging the lift and lower valve;
e. pumping fluid into the blind end of the hydraulic cylinder;
f. applying a pilot pressure to a second input of the two-position four-way valve; and
g. raising the plow with respect to a ground surface.
Lowering the plow while balancing includes the steps of:
h. activating the lift and lower valve;
i. applying a pilot pressure to a first input of the two-position four-way valve in the balance circuit;
j. pumping fluid into the rod end of the hydraulic cylinder;
k. removing the non-compressible fluid in the blind end of the hydraulic cylinder; and
l. lowering the plow toward a ground surface.
Turning off the balance circuit includes the step of:
m. disengaging the two-position valve.
When applied to load balancing plows, the present invention functions in conjunction with new or existing live power load sensed circuits and is generally designed to be used in conjunction with new or existing load sensing and gear pump central hydraulic systems. The present invention may be operated on new or existing single acting and double acting hydraulic cylinder circuits.
It is an object of the present invention to generally lessen friction between the blade cutting edge of a plow and the surface being plowed, thereby increasing blade cutting edge life.
It is a further object to allow a plow operator to raise a plow in an expedited manner while in the plow balance mode.
It is a still further object to help reduce fuel costs of the plow vehicles and to possibly permit plow vehicles to plow surfaces one or two gears higher than normal.
Because the entire weight of the plow is not resting on the blade cutting edge during balancing, it is another object of the present invention to generally cause less damage to patches, road markers, road shoulders, and softer surfaces such as gravel or dirt roads, lessen the impact to the vehicle when the plow encounters raised portions of concrete, and to help the plow follow the contours of the surface to be plowed.
It is yet another object of the present invention to transfer plow weight over the front axle of the vehicle, helping to improve steering.
These and other advantages of the present invention will be clarified in the Detailed Description of the Preferred Embodiments and the attached figures in which like reference numerals represent like elements throughout.